patch 8.2.2399: fold test fails in wide terminal

Problem:    Fold test fails in wide terminal.
Solution:   Adjust the test. (Dominique Pelle, closes #7731, closes #7739)
diff --git a/src/testdir/test_fold.vim b/src/testdir/test_fold.vim
index 895a96b..8206193 100644
--- a/src/testdir/test_fold.vim
+++ b/src/testdir/test_fold.vim
@@ -864,7 +864,7 @@
   set fdm=indent sw=2 wrap tw=80
 
   let content = [ '  foo', '  bar', '  baz',
-              \   repeat('x', 100),
+              \   repeat('x', &columns + 1),
               \   '  foo', '  bar', '  baz'
               \ ]
   call append(0, content)